1. Field of the Invention
The present invention relates to an organic electroluminescent display device, and more particularly, an organic electroluminescent display device and a method of manufacturing the same.
2. Discussion of the Related Art
In general, display devices include cathode-ray tubes (CRT) and various types of flat panel displays. However, the various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and electroluminescent display (ELD) devices, are currently being developed as substitutes for the CRT. For example, advantages of LCD devices include a thin profile and low power consumption. However, LCD devices require a backlight unit because they are non-luminescent display devices. Organic electroluminescent display (OELD) devices, however, are self-luminescent display devices. OELD devices operate at low voltages and have a thin profile. Further, the OELD devices have fast response time, high brightness, and wide viewing angles.
FIG. 1 is a circuit diagram illustrating an OELD device according to the related art.
Referring to FIG. 1, the OELD device includes gate and data lines GL and DL crossing each other to define a pixel region P. In the pixel region P, a switching thin film transistor STr, a storage capacitor StgC, a driving thin film transistor DTr and an organic light emitting diode E.
Gate and source electrodes of the switching thin film transistor STr are connected to the gate and data lines GL and DL, respectively. One electrode of the storage capacitor StgC is connected to a drain electrode of the switching thin film transistor STr and a gate electrode of the driving thin film transistor DTr, and the other electrode of the storage capacitor StgC is connected to a source electrode of the driving thin film transistor DTr and a power line PL. The drain electrode of the driving thin film transistor DTr is connected to an anode of the organic light emitting diode E. The cathode of the organic light emitting diode E is grounded.
A gate signal is applied to the gate line GL, and the switching thin film transistor STr is turned on. A data signal is applied to the data line DL, passes through the switching thin film transistor STr, stored in the storage capacitor StgC and applied to the gate electrode of the driving thin film transistor DTr. A current flowing the driving thin film transistor DTr is determined according to the data signal applied to the driving thin film transistor DTr, and the organic light emitting diode E emits light according to the current.
The organic light emitting diode E is generally formed at the substrate where the transistors STr and DTr are formed. Alternatively, the organic light emitting diode E is formed at a substrate different from the substrate where the transistors STr and DTr, and this type OELD device is referred to as a dual panel type OELD device.
FIG. 2 is a cross-sectional view illustrating a dual panel type OELD device according to the related art.
Referring to FIG. 2, a gate line (not shown) and a data line 15 are formed on a first substrate 10 and cross each other to define a pixel region P. In the pixel region P, a switching thin film transistor (not shown) and a driving thin film transistor Tr are formed. A passivation layer 25 is formed on the driving thin film transistor Tr and has a contact hole 27 exposing a drain electrode 20 of the driving thin film transistor Tr. A patterned spacer 30 is formed on the passivation layer 25. A connection electrode 35 is formed on the patterned spacer 30 and contacts the drain electrode 20 through the contact hole 27.
A first electrode 53 is formed on a second substrate 50. A buffer pattern 57 is formed on the first electrode 53 in a peripheral region of the pixel region P. A separator is formed on the buffer pattern 57 and has a trapezoidal shape. An organic light emitting layer 65 and a second electrode 70 are formed on the first electrode 53 in the pixel region P. An organic light emitting diode includes the first electrode 53, the organic light emitting layer 65 and the second electrode 70.
The OELD device 1 includes a moisture absorbent to remove a moisture permeating into the OELD device 1. The moisture absorbent is formed along a seal pattern attaching the first and second substrates 10 and 50. Alternatively, the second electrode 70 includes an aluminum layer and a calcium layer, and the calcium layer functions as the moisture absorbent. However, the calcium layer diffuses into the aluminum layer and its moisture-absorbing function is reduced. Accordingly, the organic light emitting layer 65 is deteriorated and life time of the OELD device 1 is thus reduced.
FIG. 3 is a cross-sectional view illustrating the related art OELD device where an foreign substance exists.
Referring to FIG. 3, since adhesion of a calcium layer 70b and a aluminum layer 70a is poor, the calcium layer 70b comes off the aluminum layer 70a or a second electrode 70 comes off an organic light emitting layer 65. Further, due to indraft of an alien substance 90 in a process of forming the organic light emitting layer 65, short-circuit between the first and second electrodes 53 and 70 is caused. In other words, when the organic light emitting layer 65 is formed, the indraft of the alien substance 90 is caused and the organic light emitting layer 65 is thus not formed around the alien substance 90. Accordingly, the second electrode 70 on the organic light emitting layer 65 intrudes into a portion, where the organic light emitting layer 65 is not formed, and finally contacts the first electrode 53, and thus the short-circuit is caused. The pixel region P, where the short-circuit occurs, is always in a white or black state. Accordingly, display quality and production efficiency is reduced.